MLH1 and Lynch syndrome: Lynch syndrome, also named as hereditary non-polyposis colon cancer(HNPCC), is caused by the germline mutations of four mismatch repair (MMR) related genes, including PMS2, MSH6, MLH1, and MSH2. Lynch syndrome increases the risk of endometrial and ovarian cancer, as well as colorectal, urothelial tract, stomach, and small bowel carcinoma (7).